CMS-PAS-BPH-22-003

CMS-PAS-BPH-22-003
First observation of the rare 4 $\mu$ decay of the $\eta$ meson
CMS Collaboration
25 February 2023

Abstract: The first observation of the double-Dalitz decay $\eta \rightarrow \mu^+\mu^-\mu^+\mu^-$ is reported with 2017 and 2018 data by the CMS experiment at the CERN LHC. A signal having a statistical significance well in excess of 5 standard deviations was identified using high-rate muon trigger data collected at a proton-proton collision center of mass energy of 13 TeV corresponding to an integrated luminosity of 101 fb $^{-1}$ . Using the $\eta \rightarrow \mu^+\mu^-$ decay as normalization, the branching fraction $\mathcal{B}(\eta \rightarrow \mu^+\mu^-\mu^+\mu^-) =$ (5.0 $\pm$ 0.8 (stat) $\pm$ 0.7 (syst) $\pm$ 0.7 ( $\mathcal{B}$ )) $\times$ 10 $^{-9}$ is measured, in agreement with theoretical estimates.
Links: CDS record (PDF) ; Physics Briefing ; CADI line (restricted) ; These preliminary results are superseded in this paper, PRL 131 (2023) 091903. The superseded preliminary plots can be found here.

CMS Publications